Spectral Equalization for GHA-Applied Restoration to Damaged Historical 78 Rpm Records
The authors have been engaged in the research of In-harmonic Frequency Analysis "GHA" which enables to separate desired signal-components and noise. Its primary purpose has been noise-reduction. Recently, the authors succeeded to conduct GHA in practical time length, and carried out many sound restorations of historical 78 rpm records. Thanks to GHA's sufficient separation of target signal-component from noisy object, restored signal is noise-less, however its tone quality is unnatural when it is reproduced using current audio equipments. This is due to fact that the recorded sounds were tuned to match to audio equipments in that age, therefore spectral equalization is necessary. In practice, extreme frequency emphases are required, but it had been impossible because of the existences of scratch noise. GHA-applied restoration removed theses difficulties, and equalization curve was obtained by comparing long-term spectrum of restored music with that of the same recorded music by current musicians. Generally equalizations are very complicated and were done utilizing parametric equalizer.
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